From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752365AbdHJPgn (ORCPT ); Thu, 10 Aug 2017 11:36:43 -0400 Received: from mx2.suse.de ([195.135.220.15]:57450 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751456AbdHJPgm (ORCPT ); Thu, 10 Aug 2017 11:36:42 -0400 Date: Thu, 10 Aug 2017 17:36:39 +0200 From: Michal Hocko To: Colm =?iso-8859-1?Q?MacC=E1rthaigh?= Cc: Rik van Riel , linux-kernel@vger.kernel.org, Mike Kravetz , linux-mm@kvack.org, Florian Weimer , akpm@linux-foundation.org, Kees Cook , luto@amacapital.net, Will Drewry , mingo@kernel.org, kirill@shutemov.name, dave.hansen@intel.com, linux-api@vger.kernel.org Subject: Re: [PATCH v2 0/2] mm,fork,security: introduce MADV_WIPEONFORK Message-ID: <20170810153639.GB23863@dhcp22.suse.cz> References: <20170806140425.20937-1-riel@redhat.com> <20170807132257.GH32434@dhcp22.suse.cz> <20170807134648.GI32434@dhcp22.suse.cz> <1502117991.6577.13.camel@redhat.com> <20170810130531.GS23863@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 10-08-17 15:23:05, Colm MacCárthaigh wrote: > On Thu, Aug 10, 2017 at 3:05 PM, Michal Hocko wrote: > >> Too late for that. VM_DONTFORK is already implemented > >> through MADV_DONTFORK & MADV_DOFORK, in a way that is > >> very similar to the MADV_WIPEONFORK from these patches. > > > > Yeah, those two seem to be breaking the "madvise as an advise" semantic as > > well but that doesn't mean we should follow that pattern any further. > > I would imagine that many of the crypto applications using > MADV_WIPEONFORK will also be using MADV_DONTDUMP. In cases where it's > for protecting secret keys, I'd like to use both in my code, for > example. Though that doesn't really help decide this. > > There is also at least one case for being able to turn WIPEONFORK > on/off with an existing page; a process that uses privilege separation > often goes through the following flow: > > 1. [ Access privileged keys as a power user and initialize memory ] > 2. [ Fork a child process that actually does the work ] > 3. [ Child drops privileges and uses the memory to do work ] > 4. [ Parent hangs around to re-spawn a child if it crashes ] > > In that mode it would be convenient to be able to mark the memory as > WIPEONFORK in the child, but not the parent. I am not sure I understand. The child will have an own VMA so chaging the attribute will not affect parent. Or did I misunderstand your example? -- Michal Hocko SUSE Labs